Closable nozzle body and method for closing the same

ABSTRACT

A closing element, which has an open position and a closed position and is actuated by an actuating element, is arranged in the nozzle channel of a nozzle body. In the closing position, the closing element separates a region that is at least temporarily in open communication with the injection mold, the region being able to be influenced by a second actuating element associated with the nozzle body. Due to the fact that the pressure element is arranged in the nozzle body and can be actuated independently from the nozzle body and the plastifying cylinder, a nozzle body is created and a method is provided that enable the dosing process and dwell pressure process to be separated with a compact structure.

REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority of the German patentapplication 101 13 352.9, lodged on 20.03.2002, the disclosure contentof which is herewith also made expressly the subject of the presentapplication.

BACKGROUND SECTION

[0002] A nozzle body for an injection molding machine for processingplastic materials and other plastifiable materials, such as pulverulentor ceramic materials, is known from DE 15 54 934 A, wherein a pistonshaft is moved hydraulically, which from a starting position firstdrives into the bore of a mouth ring and hence closes the nozzle openingand then serves for generating the holding pressure. Insofar this pistonshaft is at the same time closure element and pressure element. Thereina change in volume already occurs when the piston shaft is transferredinto closure position.

[0003] From PATENT ABSTRACTS OF JAPAN, vol. 014, no. 428 (M-1025), 14.Sep. 1990 & JP 02 169219 A a nozzle body is known comprising acyclically usable closure and pressure element that is axially movablein the nozzle body to influence the holding pressure which significantlyinfluences the quality of the moldings. In actuating the pressureelement, however, a change in volume occurs, what is influencing theprocess control and hence at least also the cycle by cycle reproduciblequality of the moldings.

[0004] A nozzle body having a closure element which can be usedcyclically, is also known from GB 976,369 PS. The plastified material isinjected alternately into two mould cavities, the closure elementreleasing the runner to the one mould cavity when it closes the other.One pressure cylinder unit respectively is associated with the runnersso that, as soon as the closure element closes the one runner, thepressure cylinder unit on the associated mould cavity can influence theholding pressure, whilst material is already injected again into theother mould cavity. The time advantage obtained therewith is basedhowever on the fact that two mould cavities are operated alternately sothat this device cannot be applied to a compact nozzle unit whichpossibly operates only one mould cavity.

[0005] It is known furthermore to use a shut-off nozzle on a plasticmaterial injection molding machine depending on the material, saidshut-off nozzle opening and closing the nozzle opening cyclically.Closure nozzles of this type are known for example from EP 0 322 497 A2.Closure is effected only at the end of the holding pressure phase whichis required for obtaining a qualitatively high-grade molded articlewithout sinks or shrinkholes. However, precisely in the case ofthick-walled molded articles a long holding pressure time is required,which in this respect contributes directly to increasing the cycle time.

SUMMARY OF THE INVENTION

[0006] Starting from this state of the art, the object underlying thepresent invention is to produce a nozzle body and to make available amethod which, with a compact construction, permits a separation betweenthe dosing process and the holding pressure process.

[0007] For this purpose, a holding pressure chamber is provided in thenozzle body in addition to the closure element, said holding pressurechamber being able to be influenced by a pressure element actuated inthe nozzle body by a further actuation member. It is consequentlypossible on the one hand to have an influence with the actuation memberon this chamber and on the mould cavity which is connected thereto, inorder for example to build up the holding pressure. On the other hand,dosing can already take place again at the same time however in front ofthe closure element, independently of the application of the holdingpressure. As a result, precisely with PET preforms, which generally havea large wall thickness and hence require a long holding pressure time,this long holding pressure time can be used already once again fordosing, so that the cycle time is significantly reduced. However, onlythe separation in the nozzle body is essential for the invention sothat, by external actuation, the holding pressure in the nozzle can beinfluenced, preferably can be influenced in a controlled manner, even ifno use is made of this option. A separation of holding pressure andmaterial pressure is therefore possible. The separation of dosingchamber and holding pressure chamber in the nozzle body leads howeveralso to the fact that the material to be dosed can be dosed over afairly long period of time and hence, if required, more slowly. Hence asmaller torque acts upon the screw, so that the material is subjected tofewer shear forces. This also ensures gentler handling with sensitivematerials.

[0008] Due to the actuation of the pressure element independently of thenozzle body and plastifying cylinder, the holding pressure force is nolonger dependent upon the nozzle touch force. At the same time, theimpermeability of the nozzle unit is increased.

[0009] Therein the actuation member engages on a pressure element whichis mounted so as to float in the nozzle channel. As a result, a compactconstruction is produced since the pressure element is controllable onthe one hand for influencing the holding pressure chamber but can besubjected to a flow of the newly dosed material already, without thethereby resultant pressure preventing the movement of the pressureelement.

BRIEF DESCRIPTION OF THE FIGURES

[0010] The invention is explained subsequently in more detail withreference to the enclosed figures, which show:

[0011]FIG. 1 a side view of an injection molding unit with a nozzle bodyaccording to the invention, disposed on a machine base,

[0012]FIG. 2 an enlarged section through the nozzle body according toFIG. 1 at the beginning of the mould filling phase,

[0013]FIG. 3 an illustration according to FIG. 2 near the end of themould filling phase,

[0014]FIG. 4 an illustration according to FIG. 2 at the beginning of theholding pressure phase,

[0015]FIG. 5 an illustration according to FIG. 2 at the end of theholding pressure phase,

[0016]FIG. 6,7 sections through FIG. 1 along the lines 6-6 or 7-7,

DETAILED DESCRIPTION

[0017] The invention is now explained in more detail by way of examplewith reference to the enclosed drawings. However, the embodiments onlyconcern examples which are not intended to restrict the inventiveconcept to a specific arrangement.

[0018]FIG. 1 shows an injection molding unit S of an injection moldingmachine for processing plastic materials and other plastifiablematerials, such as pulverulent or ceramic materials which machine isdisposed on a machine base 36. The injection molding unit has aplastifying cylinder 30, on the front end of which a nozzle body 10 isdisposed. Rings 20, 21 are disposed on the nozzle body as actuationelements for parts disposed in the interior of the nozzle body, saidrings being actuated by actuation members 40, 41. Other elements canalso be provided instead of the rings as long as only one reliable powerintroduction is possible into the parts disposed within the nozzle body10. The injection molding unit S plastifies the material and injects itvia the nozzle body 10 into a mould cavity of an injection mould 25. Atleast one part of the generally multi-part injection mould 25 is mountedon the stationary mould carrier 35, which according to FIG. 1 ispenetrated by the nozzle body 10 in a passage opening.

[0019] According to FIGS. 2 to 5, the nozzle body 10 has a nozzleopening 11 for injecting the plastified material into the injectionmould 25. In the nozzle opening 11, there discharges a nozzle channel 12which is connected at the other end to a plastifying cylinder 30 inwhich a feeding means 31, here a feed screw, feeds the plastifiedmaterial in the direction towards the nozzle opening 11.

[0020] Furthermore, a closure element 13 is provided for closure ifrequired of the nozzle channel 12, and is actuated by an actuationmember 40. The closure element 13 separates, in the closure position, achamber which is in open communication at least at times with theinjection mould 25. This chamber can be influenced by a furtheractuation member 41 which is associated with the nozzle body 10.

[0021] The closure element 13 hence separates, in the closure position,a chamber configured as holding pressure chamber 14 in the nozzle body10 from a dosing chamber 15 which is connected to the feeding means 31of the plastifying cylinder 30. As a result, the internal pressureand/or the volume of the holding pressure chamber 14 can be influencedindependently of the dosing taking place on the other side of theclosure element and can be controlled or regulated in the embodiment bymeans of a pressure element 16. The pressure element is disposedpreferably coaxially to an injection axis s-s in the nozzle body 10,which axis goes through the nozzle opening 11.

[0022] The pressure element 16 is disposed in the nozzle channel 12 inthe embodiment of FIGS. 2 to 7 and is moveable there in a limitedmanner. FIGS. 2 and 7 show that the ring 21 actuated by the actuationmember 41 is in operational connection by means of an actuation element51 with the pressure element 16 disposed in the nozzle channel 12. Themaximum movement possibility is limited by a slot. On its front end, thepressure element 16 has a piston 17 which acts upon the holding pressurechamber 14 and is guided in this embodiment in the closure element 13.The pressure element 16 is mounted so as to float in the nozzle channel12, so that it can itself be reliably actuated when material is againalready feeded and dosed behind the closure element 13. As a result, acompact construction is produced since the pressure element iscontrollable on the one hand for influencing the holding pressurechamber, but at the same time can be subjected to a flow already fromthe newly dosed material, without the thereby resultant pressurepreventing the movement of the pressure element.

[0023] The movement of the pressure element 16 and of the piston 17,which is securely connected thereto, leads not to a change in volumewhen the closure element 13 is open but only to a volume displacementsince the shape of the pressure element 16 and piston 17 is configuredsuch that, when the holding pressure chamber 14 and dosing chamber 15are in open communication, the pressure around the pressure element iscancelled out. The open communication is ensured by the passage channels13 a and the through-flow channels 16. Because of the floating mountingin the nozzle channel, the forces in front of and behind the pressureelement are hence cancelled out. The pressure ratios around the pressureelement remain unchanged so that the pressure element has no influenceor at least no substantial influence upon the process control. The sameapplies fundamentally also during actuation of the closure element 13.

[0024] According to FIG. 7, the pressure element 16 has through-flowchannels 16 a for the passage of plasticised material, which channelsare delimited in the embodiment by the wall of the nozzle channel 12.The through-flow channels can however also be disposed such that theycome to lie entirely in the pressure element and no contact with thewall of the nozzle channel 12 occurs. As FIGS. 2 to 5 show, the closureelement 13 is disposed in the flow direction of the plastified materialafter the pressure element 16, however its piston 17 lies parallel tothe pressure element 16. The closure element 13 is likewise disposed inthe nozzle channel and has passage channels 13 a for the passage ofplastified material into the holding pressure chamber 14. These passagechannels 13 a, which are present in the open position according to FIG.6, are closed by an axial movement of the closure element 13 on the wallof the nozzle channel 12, preferably at the end-side on the nozzle head18. Other closure possibilities are possible but this embodiment has theadvantage that a relatively large sealing face is produced with a smallclosure path.

[0025] In this embodiment, the device operates in the following manner:

[0026] The state at the beginning of the filling phase is illustrated inFIG. 2. The feeding means 31 is still located in the withdrawn state onthe right in FIG. 2. In the chamber in front of the feeding means 31,plastified and dosed material is situated. The pressure element 16 ismoved further forwards at the end of the last cycle, whilst the closureelement is transferred to the right into its open position. If thefeeding means 31 is now moved to the left in FIG. 2, then firstlymaterial is conveyed via the through-flow channels 16 a and also thepassage channels 13 a into the injection mould 25.

[0027] An illustration according to FIG. 3 is produced towards the endof the filling phase. On the one hand, the pressure element 16 wasthereby withdrawn or pushed to the right so that a holding pressurechamber 14 is formed in front of the piston 17 of the pressure element16. The closure element 13 is still located in the open position. Themovement of the pressure element 16 and of the piston 17, which issecurely connected thereto, leads not to a change in volume when theclosure element 13 is open but only to a volume displacement. Because ofthe floating mounting in the nozzle channel, the forces in front of andbehind the pressure element are hence cancelled out. The pressure ratiosaround the pressure element remain unchanged so that the pressureelement has no influence upon the process control.

[0028] However, the closure element 13 is also configured such that thesame forces are applied in front of and behind the closure element inthe open position. The movement of pressure element 16 with piston 17and also the movement of the closure element therefore have above all noinfluence upon the injection molded part.

[0029] This pressure equalization only changes when the closure elementaccording to FIG. 4 is transferred to the left into the closure positionby the actuation element 50 in conjunction with the ring 20 and theassociated actuation member 40. The channel between the closure element13 and the nozzle head 18 which is still present there in FIG. 3 ishence closed. What is thereby advantageous is the relatively longsealing face relative to a simple closure of the passage channel 13 a.

[0030] The holding pressure now applies on the one side of the closureelement in the direction of the injection mould and, on the other side,the dosing pressure. However, the pressure ratios at the pressureelement 16 have also changed since the piston 17 of the pressure element16 is now subjected to holding pressure. Hence a separation is effectedbetween the holding pressure chamber 14 and the dosing chamber 15 whichis present behind the closure element. If new material is now dosed, auniform pressure is set in front of the pressure element in the regionof the nozzle channel 12 and between closure element and pressureelement 16, however since the piston 17 is subjected to a differentpressure, the forces around the pressure element 16 are no longercancelled out. Since the holding pressure and hence the actuation of thepressure element 16 with piston 17 is effected from the outside via theactuation element 50 and the ring 20 due to the actual values of aninternal pressure sensor preferably in the injection mould, this ishowever without consequence for the injection molded part since this isnot influenced by the pressure ratios around the pressure element.

[0031] As a result, the pressure element 16, although it is located inthe nozzle channel 12, can move freely as an element which is mounted soas to float. Whilst material is therefore dosed for the next cyclealready in the dosing chamber 15, the holding pressure can still beapplied from the holding pressure chamber 14 by actuation of thepressure element by means of ring 21 and actuation element 51. Themovement of the pressure element leads not to a change in volume butonly to a volume displacement so that dosing can take place neverthelessin a uniform manner behind the closure element. Hence, simultaneousdosing and application of holding pressure is therefore possible so thatthe holding pressure time, the length of which normally definitivelydetermines the cycle e.g. in the case of PET preforms, can be usedalready for dosing the next cycle. The separation thus offered betweendosing and holding pressure is possible in the nozzle body 10 by meansof the externally actuated elements.

[0032] According to the method, a cyclical separation of a chamber inthe nozzle body 10 and influencing of this chamber by means of a furtheractuation member 41 is effected. The holding pressure chamber 14 anddosing chamber 15 are thereby configured such that the holding pressurechamber 14 can be influenced in a controlled or regulated manner duringthe holding pressure phase, whilst the dosing of the next cycle canbegin at the same time already behind the closure element.

[0033] It goes without saying that this description can be subjected tothe most varied of modifications, changes and adaptations which act asequivalents with respect to the dependent claims.

1. Nozzle body (10,10′) for an injection moulding machine for processingplastic materials and other plastifiable materials, having a nozzleopening (11) for injecting the plastified material into an injectionmould (25), at least one nozzle channel (12,12′) discharging in thenozzle opening (11) for connection to a plastifying cylinder (30) atleast one closure element (13,13′), which is to be actuated by anactuation member (40) and is disposed in the nozzle body, for closure,if required, of the nozzle channel (12,12′), the closure element(13,13′) separating in closure position a holding pressure chamber (14)which is in open communication at least at times with the injectionmould (25) at least one further actuation member (41,41′) associatedwith the nozzle body (10,10′) for influencing the holding pressurechamber by means of a pressure element (16,16′), characterised in thatthe pressure element (16,16′) is disposed in the nozzle body (10,10′)and is actuatable independently of the nozzle body and the plastifyingcylinder (30).
 2. Nozzle body according to claim 1, characterised inthat the closure element (13,13′) separates in closure position theholding pressure chamber (14) from a dosing chamber (15) which isconnected to a feeding means (31) of a plastifying cylinder (30). 3.Nozzle body according to claim 1 or 2, characterised in that the furtheractuation member (41,41′) controls the internal pressure and/or thevolume of the holding pressure chamber (14) by means of the pressureelement (16,16′) which is preferably in one piece with a piston (17). 4.Nozzle body according to one of the preceding claims, characterised inthat the pressure element (16,16′) is disposed so as to move in alimited fashion coaxially to an injection axis (s-s) going through thenozzle opening (11), in the nozzle channel (12) of the nozzle body (10,10′).
 5. Nozzle body according to one of the preceding claims,characterised in that, when the closure element (13) is open, thepressure acting as a result of the plastified material being underpressure upon the outer faces of the pressure element (16) with piston(17) from the direction of the nozzle opening (11), i.e. by pressureacting from the front, is equal to that upon the outer faces of thepressure element from the rear as a result of the pressure of theplastified material, so that the forces around the pressure element (16)are cancelled out.
 6. Nozzle body according to one of the precedingclaims, characterised in that the piston (17) acting on the holdingpressure chamber (14) is guided in the closure element (13).
 7. Nozzlebody according to one of the preceding claims, characterised in that thepressure element (16) is movable in the nozzle channel (12) without achange in volume.
 8. Nozzle body according to one of the precedingclaims, characterised in that the pressure element (16) comprisesthrough-flow channels (16 a) for the passage of plastified material,said channels being delimited by the wall of the nozzle channel (12). 9.Nozzle body according to one of the preceding claims, characterised inthat the closure element (13) is disposed in the flow direction of theplastifiable material after the pressure element (16) but parallel toits piston (17).
 10. Nozzle body according to one of the precedingclaims, characterised in that the closure element (13) is disposed inthe nozzle channel (12) and has passage channels (13 a) for plastifiedmaterial in the open position.
 11. Nozzle body according to claim 10,characterised in that the passage channels (13 a) can be closed by anaxial movement of the closure element (13) on the wall of the nozzlechannel (12), preferably at the end-side on the nozzle head (18). 12.Nozzle body according to one of the preceding claims, characterised inthat, when the closure element (13) is open, the pressure acting as aresult of the plastified material being under pressure upon the outerfaces of the closure element (13) from the direction of the nozzleopening (11), i.e. by pressure acting from the front, is equal to thatupon the outer faces of the pressure element from the rear as a resultof the plastified material so that the forces around the pressureelement (16) are cancelled out even when the same is moving.
 13. Nozzlebody according to one of the claims 1 to 4, characterised in that thepressure element (16′) in the nozzle body (10′) is disposed in a regionwhich is separate from the nozzle channel (12′).
 14. Nozzle bodyaccording to claim 13, characterised in that the pressure element (16′)has a piston (17) acting upon the holding pressure chamber (14), saidpiston being guided in the nozzle body (10′).
 15. Nozzle body accordingto one of the claims 13 or 14, characterised in that passage openings(19) are provided for plastified material, said openings being guided inthe nozzle body (10′) around the pressure element (16′) at a spacingfrom the pressure element (16′).
 16. Nozzle body according to one of theclaims 13 to 15, characterised in that the closure element (13′) closesthe nozzle channel (12′).
 17. Nozzle body according to one of the claims13 to 16, characterised in that the closure element (13′) is disposed inthe flow direction of the plastified material in front of the pressureelement (16′).
 18. Method for closing a nozzle body (10,10′) accordingto one of the preceding claims, a chamber being separated cyclically inthe nozzle body (10,10′) by means of a closure element (13,13′) and, inthe closure position of the closure element, the holding pressurechamber (14) being influenced by means of a further actuation member(41,41′) with a pressure element (16,16′), characterised in that thepressure element (16,16′) in the nozzle body (10,10′) is actuatedindependently of the nozzle body and the plastifying cylinder (30). 19.Method according to claim 18, characterised in that the closure of thenozzle channel (12,12′) is effected by means of the closure element(13,13′) before the holding pressure phase and in that the furtheractuation member controls the holding pressure in the injection mould(25) by influencing the holding pressure chamber (14).
 20. Methodaccording to one of the claims 18 to 20, characterised in that, duringinfluencing of the chamber in the closure position of the closureelement (13,13′), plastified material can be dosed simultaneously in thedosing chamber (15).
 21. Method according to one of the claims 19 to 22,characterised in that the pressure element (16) and/or the closureelement (13) is movable in the nozzle channel (12) when the closureelement is open, without a change in volume of the plastified materialsurrounding the pressure element.